Cell: The Unit of Life

| 115



Chromatophores are other membranous extensions in some

prokaryotes (e.g. cyanobacteria). They contain pigments (AIPMT 1999)

3. Nucleoid

It is formed of non-membranous (naked) circular genomic DNA

(single chromosome/ Genetic material) & protein. (AIPMT 2013)

Many bacteria have small circular DNA (plasmid) outside the

genomic DNA. It gives some unique phenotypic characters (e.g.

resistance to antibiotics) to bacteria

4. FLAGELLA

These are thin filamentous extensions from the cell wall of

motile bacteria. Their number and arrangement are varied in

different bacteria.

Bacterial flagellum has 3 parts – filament, hook and basal

body. The filament is the longest portion and extends from

the cell surface to the outside.

5. Pili and Fimbriae

These are surface structures that have no role in motility.

(NEET-II 2016)

Pili (sing. Pilus) are elongated tubular structures made of a

special protein (pilin).

Fimbriae are small bristle like fibres sprouting out of the cell.

In some bacteria, they help to attach the bacteria to rocks in

streams and to the host tissues.

(AIPMT 2015)

6. Ribosomes

They are associated with plasma membrane of prokaryotes.

They are about 15 nm by 20 nm in size.